X-ray computed tomography (CT) apparatuses are each provided with an X-ray detector that includes a plurality of X-ray detection elements. In some cases, X-ray detection elements are arranged in positions shifted by ¼ of a channel in a channel direction. This is called a ¼ offset arrangement.
The recent development of X-ray CT apparatuses has realized selective use of a plurality of detector resolution modes such as a normal mode for generating images with a normal resolution and a high-resolution mode for generating images with a higher resolution than the normal mode. This type of X-ray CT apparatus changes units of a channel that outputs X-ray detection signals according to each mode. For example, in a high-resolution mode, the X-ray CT apparatus outputs X-ray detection signals from X-ray detection elements, while setting a single channel to each of X-ray detection elements. In a normal mode, the X-ray CT apparatus causes the X-ray detection elements to output X-ray detection signals, while setting a single channel to a predetermined number of adjacent X-ray detection elements. For example, in the normal mode, the X-ray CT apparatus classifies two X-ray detection elements as a single channel.
In this case, a position of a channel's center varies between the high-resolution mode and the normal mode. For example, if the X-ray detection elements are arranged ¼-offset under the high-resolution mode, their shift amount turns out to be as little as ⅛ of a channel under the normal mode. That is, a ¼-offset arrangement of X-ray detection elements is unrealizable in the normal mode. Therefore, if the X-ray detection elements are arranged ¼-offset in accordance with the high-resolution mode, the resolution of images generated in the normal mode is deteriorated as compared with the case where the X-ray detection elements are arranged ¼-offset in accordance with the normal mode.